Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
413 PM CDT sun Mar 16 2014
Short term...(this evening through monday)
issued at 410 PM CDT sun Mar 16 2014
The polar high will continue progressing eastward this afternoon
as upper level moisture begins to back-fill from the west. Middle and
high level cloudiness will be on the increase so filtered
sunshine can be expected early this evening. This cloud cover is
associated with an area of strong warm air advection approaching
from the west.
Strong SW winds at the 850h level will get going tonight
behind the passage of a warm front. The lift provided by this
advection...coupled with stronger upper level divergence...and fn
vector convergence will skim the northern portion of the County Warning Area
tonight through early tomorrow morning. Moisture and saturation is
more questionable...especially south. Currently thinking is that
the better forcing along the northern periphery of the County Warning Area
/especially in northwest Wisconsin/ should be able to overcome the
moisture challenges and saturate the column. Did keep some slight
chance probability of precipitation in the forecast just south of the best forcing...but
drier low level flow really looks to hinder the chance of seeing
any measurable precipitation there. Temperatures will be held in
check tonight as warm southerly winds and overcast skies hold
overnight temperatures nearly steady.
Temperatures will warm up quite a bit across western Minnesota
with temperatures shooting up into the 50s downstream of the
Buffalo Ridge. Much cooler temperatures will be seen across the
eastern half of the forecast area /the same area as the current snowpack/.
Long term...(monday night through sunday)
issued at 318 PM CDT sun Mar 16 2014
Main focus remains on the prolonged winter event expected to
impact the area Monday night through Wednesday. Still much model
uncertainty among the models and lack of run-to-run consistency
within several models...so confidence still not entirely high in
the exact placement and timing of p-type and amounts.
Since the sref and NAM are still considered outliers in being too
far north with the progression of the surface low and related features...
including very pronounced quantitative precipitation forecast and warm air intrusions...the
forecast has taken a mainly GFS/European model (ecmwf) look to it. However...even
between those two models...it needs to be seen which primary surface
low will be the main player. The 12z GFS is more of a clipper-type
origin with some plains-hybrid effects as it swings from SW Canada
across the northern plains and gets picked up by a digging upper level
trough. The 12z ec depicts more of a Colorado/Kansas low that shifts northeastward into
the Great Lakes while also being picked up by an upper trough...
although not as intense. This leads to the GFS showing more quantitative precipitation forecast
and less warm air intrusion while the ec is drier but contains
warmer air. Going with a blend of the two leads to quantitative precipitation forecast...and hence
snowfall and icing amounts...that are less than Winter Storm Watch
criteria through the period but also contains much uncertainty and
a very changeable forecast. Therefore...have continued to use the
hazardous weather outlook /hwo/ to highlight this event.
So...based on the forecast as it currently is...which is not much
of a change from the previous forecast...this is how things look
to develop. Precipitation will develop over northwestern portions of the County warning forecast area Monday
night as a rain or rain/icy mix as enough warm air within the blyr
will be available to promote the wintry mix for northern portions of
the County warning forecast area. The icy mixture will the spread southeastward overnight Monday night
into Tuesday morning...affecting much of central-eastern Minnesota into western WI with
the icy mix around the morning rush hour. Not looking for a lot of
quantitative precipitation forecast at this point but there is growing confidence at least in the
aspect of having icy precipitation early-middle Tuesday morning. As warmer air is
wrapped around the southern-eastern fringes of the surface low into southern-central
Minnesota...the p-type will change to all rain for much of the mpx
County warning forecast area...save the far northwestern portion which will have highs only
hitting the freezing mark so if not -sn then a -ra/-sn mix is
expected. The surface low will then traverse to the southeast of the area Tuesday
evening...bringing in a colder surge of air on its backside at the surface
while northwest flow aloft takes hold on the backside of the digging
trough. This will change over the p-type from -ra to -sn from northwest to
southeast Tuesday evening into the night hours. With additional deeper moisture
and possibly a negatively tilted trough which would enhance
lift...some heavier snow is possible Tuesday evening through Tuesday night
before the precipitation winds down during the day Wednesday. Some snow amounts
in the 3-6 inch range is certainly possible in north-central Minnesota Tuesday
into Wednesday...but trying to pin this down at this time is highly problematic
as models are indicating as high as 6-10 inches in central Minnesota with
higher amounts going into the weather forecast office fgf and dlh areas.
This system then rotates its way out of the region during the day on
Wednesday...but the respite will be brief as another system looks to
bring a wintry mixture of precipitation Thursday night through Friday...
followed by another quick-hitting system for next Sunday. None of
these systems looks to bring much in the way of quantitative precipitation forecast but each one
does have the potential for a rain/snow/icy mix at times along
with minor snowfall accumulations.
Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 104 PM CDT sun Mar 16 2014
Quiet aviation period ahead with VFR conditions expected
throughout. Warm air advection ensues later today through the
night across the area as a warm front pushes across the region
from west to east. Only mention of precipitation was the possibility of
-sn at axn and stc...otherwise dry. Confidence remains low in
actually seeing any -sn at stc so kept the prob30 going for
tonight. High clouds building across the area will be followed by
middle level cloudiness...but all ceilings expected to be VFR. Winds
from the southeast will turn more southerly and increase behind
the front...and become gusty tomorrow.
Kmsp...still expecting any -sn to remain north of the Airport as
low level dry air is too much to overcome. VFR throughout the
period with blustery south winds through the day tomorrow.
/Outlook for kmsp/
Monday...VFR with MVFR and -ra/snow possible late. Winds S 10g15kts.
Tuesday...MVFR with IFR and -sn likely possibly mixed with ra/fzra.
Winds NE 10g20kts.
Wednesday...MVFR with IFR and snow possible early...then VFR. Winds northwest